The present invention relates to treating black tea leaves for providing aqueous beverage extracts which have minimal turbidity in cold water.
Black tea for preparing hot and cold beverages historically has been obtained by subjecting freshly picked tea leaves to various processing steps which include a fermentation step which employs enzymes which are naturally present in the fresh tea leaves. Under appropriate conditions, the enzymes effect an oxidation reaction with various chemical compounds present in the tea which results in providing the organoleptic and aesthetic characteristics associated with aqueous beverage extracts obtained from black tea. In addition, the art discloses processes for treatment of green tea to obtain a treated tea said to have characteristics of black tea by subjecting green tea to oxidation processes, such as disclosed, for example, in U.S. Pat. Nos. 2,975,057, 3,445,236 and 3,484,246.
Aqueous extracts obtained from black tea contain substances, believed to be primarily polyphenolic compounds and complexes of polyphenolic compounds and caffeine, as discussed in the art, responsible for the desirable organoleptic and aesthetic characteristics of the extracts. Although these substances are readily soluble in hot water, i.e., boiling water, at beverage concentrations and at temperatures when the beverage is consumed hot, i.e., above about 60.degree. C., when the extracts are cooled to room temperature and below, these substances are, at most, only partially soluble in the water of the extract. Thus, the cooled extracts have a "cloudiness" which occurs from these substances being in a form of solids in suspension and from precipitated sediment. The cloudiness, which is not aesthetically acceptable, is known conventionally in the art as "turbidity", and the solids also are described as "tea cream".
Various methods and means have been proposed, attempted and utilized in the art to provide extracts which have minimal turbidity in cold water, the most simple being cooling a hot water extract of black tea so that a precipitate will form. The solids then are removed from the extract by means such as filtration or centrifugation. However, it long has been recognized that such processes are unacceptable because removal of the solids from the extract not only eliminates valuable organoleptic and aesthetic components, but also results in valuable yield losses.
Thus, various methods have been proposed, attempted and utilized to solubilize the substances which create the turbidity problem. Such efforts include, after aqueous extraction of black tea leaves, oxidizing the extract obtained, particularly under alkaline conditions, in the presence of oxygen, such as in U.S. Pat. No. 3,163,539. As also disclosed in that patent, a tea cream precipitate may be separated from the extract and oxidized. Then the resultant oxidized, solubilized material is added back to the extract.
Further methods to treat separated tea cream under alkaline conditions also are referred to and disclosed in U.S. Pat. Nos. 3,151,985 and 3,451,823 and in Canadian Patent No. 927,189, the latter of which also discloses treating the oxidized cream with sulfur-containing compounds to obtain improved color characteristics. On the other hand, U.S. Pat. No. 3,787,590 discloses performing oxidation of tea cream in the absence of added alkali in a manner so the oxidation will take place at a pH in the range of from about 2 to about 3.5.
Other efforts in the art to reduce turbidity and improve clarity of black tea extracts include, as disclosed in U.S. Pat. No. 3,787,582, adding a pectinage enzyme preparation to aqueous black tea extracts which is said also to reduce foaming of instant water-soluble extracts prepared therefrom and also to improve color; treating the extracts with catechins, as disclosed in U.S. Pat. No. 4,680,193; adding a water-soluble caseinate to the extracts, as disclosed in European Patent Application Publication No. 0 133 772; and adding tannase or tannase producing molds to the extracts, as disclosed in British Patent Specification 1 249 932 and in U.S. Pat. No. 3,959,497, respectively.
Additionally, U.S. Pat. No. 4,051,264 discloses a process for treating green tea with tannase which is said to, after a traditional fermentation process, yield treated leaves which provide an extract having a reduced level of cold water insoluble solids as compared with an extract obtained from leaves not so treated.
It also has been disclosed that black tea leaf may be treated to prepare a product having greater solubility than conventional black tea extracts by treating the leaf with an enzyme solution containing tannase and at least one "cell wall digesting" enzyme, such as cellulase, pectinase, papain or hemicellulase, as disclosed in U.S. Pat. No. 4,639,375.
Finally, Nagalakshmi, et al., Food Chemistry 13 (1984) 69-77, disclose that the amount of tea cream solids in extracts of black tea may be reduced by incorporating various carbohydrates into green tea leaves and then fermenting the treated green tea to obtain black tea.